The present invention concerns a thrust reverser for a bypass turbofan type turbojet engine. The turbojet engine is fitted at the rear of the fan with a duct to channel the so-called cold bypass flow, the duct consisting of an inner wall enclosing the structure of the engine proper at the rear of the fan and of an outer wall of which the upstream portion is continuous with the engine cowling enclosing the fan. This outer wall can simultaneously channel the bypass flow and the downstream primary flow rearward of the so-called hot, primary flow exhaust in the case, for instance, of mixed or confluent flows, but in other cases the outer wall may only channel the bypass flow, specifically in the case of separated flow cowlings.
Furthermore, a wall may fair the engine exterior, that is the outside of the cowling enclosing the fan and the outside of the outer wall of the above-described duct, in order to minimize power plant drag. This would be the case for power plants mounted on the outside of the aircraft, in particular when these power plants are affixed underneath the wings or to the rear of the aircraft fuselage.
French patent application No. 9609705 published as FR 2 752 017 on Feb. 6, 1998 discloses an embodiment illustrated in FIG. 1 of the attached drawings of a thrust reverser having scoop-forming doors, hereinafter called scoop doors, said thrust reverser being associated with a bypass turbojet engine.
As illustrated in FIG. 1, the thrust reverser includes a movable subassembly and a stationary structure. The movable subassembly includes hollow doors 3 that form a movable part 2 and, in the forward thrust mode, also form an outer portion of the cowling. The fixed structure includes an upstream part 6 upstream of the doors 3, a downstream part 7 downstream of the doors 3 and longitudinal beams (not shown) connecting the upstream part 6 to the downstream part 7, the fixed structure also constituting a part of the outer fairing.
The doors 3 are located along a circumference of the outer fairing of the cowling and are pivotally mounted within a zone between their side walls on the beams connecting the downstream part 7 to the upstream part 6 of the outer fairing. Side walls located on opposite sides of the doors connect the outer surface or outer panel 4 of the doors 3 that form a portion of the outer cowling to the inner part 5 of the doors 3 that form an outer portion of the bypass duct wall.
The fixed upstream part 6 comprises a forward frame 8 which may be used as a support for control means used to actuate or displace the doors 3, for example linear actuators. These control means displacing the doors 3 likewise can be located on other sides of the periphery of the door 3, for example downstream of the door. In such a case, the support for the control means will be provided by the fixed downstream part 7.
When driven into a thrust reversal position, the doors 3 pivot in such a manner that a portion of the doors upstream of the pivots 9 more or less fully obstruct the bypass duct while opening a passage in the external cowling in such a way as to channel the bypass flow 13 and 14 respectively laterally or outwardly relative to the duct axis through, on one hand, the duct 10 in the door 3 and, on the other hand, through the opening between the edge of the opening and the outside surface 4 of the door 3. The downstream door portion moves to the vicinity of the external side of the cowling in the thrust reverse position. The door angular excursion is adjusted to assure a bypass flow passage and to strongly reduce and even suppress the forward thrust from this flow, while generating a reverse thrust by producing an upstream directed flow component.
Because of the constraints on the excursion of the door dictated by aerodynamic considerations, including the dimensions of the flow passages opened by the upstream door portion in the thrust reversal position, the above-described thrust reverser includes a downstream protruding shape 12 downstream of the forward frame 8. A more or less pronounced stagnant air zone 11, typically found in conventional door designs in this zone, effectively reduces the cross-section of the passage for flow 14 while limiting the angle of reversal of flow 14 toward the front of the cowling. This stagnant zone 11 effectively forms an aerodynamic plug reducing the effective cross-section of the reverse flow stream.
Some aerodynamic degradation also is caused by this limitation on the effective cross-section of the thrust reversal flow. The thrust reversal flow 14 deflected outwardly by the outer surface 4 of the door is affected by the aerodynamic plug where the flow 14 meets the outward flow 13b exiting the door conduit 10. The flow 14 is caused by the plug to interfere with the reverse thrust flow 13b in a forward direction by merging against such flow.